1. Field
The disclosure relates to a non-volatile memory device and, more particularly, to a programming method of a non-volatile memory device having a charge storage layer between a gate electrode and a semiconductor substrate.
2. Description of the Related Art
A non-volatile memory device is distinguished from a volatile memory device in that previous data is maintained even though supplied power is cut off.
Generally, the non-volatile memory device has a charge storage layer between a semiconductor substrate and a gate electrode. According to the structure of the charge storage layer, the non-volatile memory devices are roughly classified into floating gate type memory devices and MNOS type memory devices.
The floating gate type non-volatile memory device has a structure that includes a tunnel dielectric layer, a floating gate, an intergate insulating layer, and a control gate, which are stacked on a semiconductor substrate. The floating gate where charges are stored is formed of a conductive layer.
The MNOS type non-volatile memory device has a structure of MNOS (metal nitride oxide semiconductor) or MONOS (metal oxide nitride oxide semiconductor). That is, it has a structure that includes a dielectric layer between a semiconductor substrate and a gate, serving as a charge storage layer. The MNOS type non-volatile memory device stores data by using a trap site inside the dielectric layer, and a trap site exiting in the interface, for example, the interface between the dielectric layer and the semiconductor substrate. Specifically, in the case that the gate is formed of a polysilicon layer, it has a structure of SONOS (silicon oxide nitride oxide silicon). Chan, et al. introduced “SONOS type memory devices” (IEEE Electron Device Letters, Vol. 8, No. 3, p. 93, 1987).
The programming of the non-volatile memory device is performed mostly using hot electrons. The current consumed during the programming ranges from dozens of μA to hundreds of μA. As such, with this large consumption of program current, the function and efficiency of the device are deteriorated. For example, in an embedded device, it is difficult to adjust a predetermined program current specification. 10 μA to 15 μA of program current per cell is required in order to use a typical merged flash logic, but it is difficult to satisfy such a requirement in the programming method using hot electrons. In a stand-alone device, since the size of a charge pumping circuit needs to be increased in order to supply a program current, chip size is increased, thereby deteriorating its cell efficiency.